The field of this invention is carbocyclic amines. More particularly, this invention relates to an improvement in the known processes for making para-nitrodiphenylamines.
Para-nitrodiphenylamines are useful intermediates in the formation of rubber antioxidants and antiozonants. Their generic formula is as follows: ##STR1## R and R.sup.1 are selected from the group consisting of hydrogen and alkyl radicals (1-9C). R.sub.2 and R.sub.3 are selected from the group consisting of hydrogen, alkyl radicals containing from 1 to 9 carbon atoms (1-9C), alkoxy radicals 1-9C and cycloalkyl radicals 5-6C.
These compounds are synthesized by reacting: (1) para-halonitrobenzenes conforming to the following structural formula: ##STR2## wherein X is a halogen selected from the group consisting of chlorine and bromine; (2) with a primary aromatic amine of the following structural formula: ##STR3## (3) in the presence of a neutralizing agent (which neutralizes the acid formed and which is usually charged in a slight excess, 2-12%, over theoretical amount) selected from the group consisting of alkali metal salts, oxides of alkali metals, and alkali metal hydroxides; (4) in the presence of copper or a copper salt catalyst (e.g. cuprous cyanide) at a concentration of at least 0.1 parts by weight per 100 parts by weight of the para-halonitrobenzene; (5) at a temperature of 170.degree. to 215.degree. C.; (6) at a pressure of from atmospheric to about 300 kPa (kilopascals); and (7) with an excess of primary aromatic amine of from 5 to 300%. A preferred pressure is about atmospheric pressure.
There is an alternative process to the above catalytic process for making para-nitrodiphenyl amines which is called the formanilide process, which is similar to the above catalytic process except for the following: (1) there is no catalyst; (2) instead of a primary aromatic amine, the second reactant is a formanilide of the following structural formula: ##STR4## (3) the temperature range of the reaction is from 120.degree. to 195.degree. C.; and (4) there is from 0 to 100% excess formanilide over the amount theoretically necessary to react with the para-halonitrobenzene.
The catalytic process is described in British Pat. Nos. 798,148; 834,510; German Pat. No. 185,663 and U.S. Pat. No. 3,155,727. The reaction which occurs is believed to be, ##STR5## (4,4'-dinitrotriphenylamines) are also formed in small amounts.
An example of the neutralizing process is, EQU HX + K.sub.2 CO.sub.3 .revreaction. KHCO.sub.3 + KX VII EQU 2khco.sub.3 .fwdarw. h.sub.2 o + co.sub.2 .uparw. + k.sub.2 co.sub.3 viii
this step serves the important function of removing the acid (HX) which can impede the main nucleophilic substitution reaction.
The formanilide process is described in German Pat. No. 1,056,619 and is believed to proceed by the following reaction: ##STR6##
The neutralization of the HX is the same as reactions VII and VIII above.
A moderately good yield of para-nitrodiphenylamine (75-90%) can be obtained by the catalytic process; but the reaction times are somewhat long (10-24 hours). The best yield are obtained at temperatures lower than 205.degree. C. and at times in excess of 12 hours. The product quality suffers by having a fair amount of tars and by-products in the final product. The work-up or purification of this product is faster than in the formanilide process, and the COD level of the wastewater stream resulting from this work-up is generally less than that resulting from the work-up of the formanilide process.
The use of formanilide in the catalytic process woth CuO catalyst is found in U.S. Pat. No. 3,313,854.
In the work-up after the catalytic process reaction is complete, the reaction mixture is cooled to below about 100.degree. C., and water and an organic liquid which azeotropes with water are added to the reaction mixture. The amount of water added is sufficient to dissolve the inorganic salts present. The azeotroping organic liquid is added in sufficient quantity to facilitate a rapid separation of the aqueous and organic phase. The resulting mixture is agitated at an elevated temperature (e.g. approximately 85.degree. C.) for a time sufficient to transfer most of the inorganic salts to the water phase. The agitation is stopped, and the aqueous and organic phases are permitted to separate. The aqueous phase containing inorganic salt ions (e.g. cuprous, cyanide, potassium, chloride and carbonate), the azeotroping organic liquid (e.g. toluene or benzene), aniline, and some para-chloronitrobenzene, flows to effluent treatment. This water wash and decant step is followed by an azeotropic distillation. After this azeotropic drying step, the last traces of inorganic salts come out of solution, and they can be removed by filtration of the hot organic phase.
On the other hand, the work-up of the formanilide process involves the steps of: (1) cooling the mixture below about 100.degree. C.; (2) adding an organic liquid which forms a minimum boiling azeotrope with water; (3) adding water and an hydrolysis catalyst (e.g. 15% NaOH); (4) agitating the resulting mixture at an elevated temperature (e.g. approximately 95.degree. C.) for a time sufficient to hydrolize the excess formanilide remaining (e.g. 11/2 hours); (5) stopping the agitation and permitting the aqueous and organic phases to separate; and (6) decanting the aqueous layer, containing inorganic salts (e.g. KCl, NaOH and unreacted K.sub.2 CO.sub.3), alkali metal formates (e.g. potassium and sodium formate), aniline, para-chloronitrobenzene, formanilide, and some of the azeotroping organic liquid. This decanted aqueous phase flows to effluent treatment. It is higher in COD than the corresponding stream from the catalytic process, principally because formates and formanilide contained therein are much more soluble in water than aniline (the main organic in the catalytic process effluent stream). Most of the aniline obtained from the hydrolysis remains in the organic phase and may be recovered by distillation later in the process.
The above procedure can be followed by a hot water wash. This consists of adding water to the organic phase and agitating the two phases at an elevated temperature (85.degree.-90.degree. C.) and thereafter decanting the two phases to remove any residual inorganic salts and unhydrolyzed formanilide in the water phase which is sent to effluent treatment.
The formanilide process reaction normally takes from 4 to 9 hours with a product yield of from about 85 to 98%. The best yields are obtained at the lower temperatures, but require the longest times. However, the hydrolysis reaction in the work-up at the end of the reaction is time consuming and reduces the time advantage that the formanilide process has over the catalytic process.
The following patents represent efforts to use polar solvents as an aid in the synthesis of nitrodiphenylamines: U.S. Pat. No. 3,053,896 (water); U.S. Pat. No. 3,055,940 (dimethylformamide (DMF) and hexamethylphosphoramide); U.S. Pat. No. 3,121,736 (tetrasodium salt of ethylenediaminetetraacetic acid (EDTA), autoclave conditions, 24 hours, 210.degree. C., 80% yield); U.S. Pat. No. 3,277,175 (dimethylsulfoxide); British Pat. No. 839,420 (DMF and hexamethyl phosphoramide); British Pat. No. 850,870 (salicylates and methylsalicylamide); British Pat. No. 877,884 (water and 60 atmospheres pressure); and Belgian Pat. No. 618,462 (DMF).
Several of the foregoing patents disclose the use of DMF in the reaction. There are certain problems involved with the use of DMF which are: (1) DMF boils at 153.degree. C. and distills with the volatiles (e.g., aniline, water and toluene) in the reaction mixture into the reflux column and condenser with which the reactor is normally fitted. It is thereafter necessary to recycle the DMF back to the reactor from an overhead receiver. This condition makes constant monitoring of the volatiles necessary to ensure ideal reaction conditions. (2) DMF is readily absorbed through the skin and can carry impurities with it. The health hazards connected with handling primary aromatic amines (e.g. aniline) and such compound as cuprous cycanide in DMF are manifest.
There is also a problem connected with the presence of water in the system. As can be seen from reaction VIII, the presence of water in sufficient quantity will greatly retard the reaction. That is why the reactor is normally fitted with a refluxing apparatus. The water can be removed by boiling it off. This "drying" is aided by the presence of the azeotroping organic liquid.
Japanese Patent Publication No. 70/09452 discloses the use of diethylformamide and cupric iodide as a catalyst system in a catalytic type process.
Netherlands application No. 65/06527 (Nov. 23, 1965) discloses the use of amides (e.g. acetanilide) in a catalytic type process.
Belgian Pat. No. 844,851 describes the solubilization of alkali metal salts in organic solvents by the use of polyethylene glycol ethers having the formula EQU R" O --CH.sub.2 CH.sub.2 O .sub.n R'
in which n is 6 or more, and R" and R' are alkyl, aryl or cycloalkyl. This patent also discusses the use of macrocyclic polyethers having about 4-20 oxygen atoms, each being separated by two carbon atoms as solubilizing agents for inorganic salts. The above solubilizing agents are described in the Belgian patent as useful in catalyzing substitution reactions.
The present invention is a solution to the problem of long reaction times which avoids the disadvantages inherent in the use of DMF or water, and at the same time it results in higher yields and fewer by-products.